Yes, there was an RFC to add trailing commas to all list syntax in PHP 7.2. Unfortunately due to an oversight on my end, the vote for function calls and function declarations was combined into one vote so the vote failed (but just barely!)

I was contacted by many “no” voters saying that they would have voted “yes” for function calls, but “no” for function declarations. This RFC proposes allowing a trailing comma in function call syntax only.

We are allowed to put this feature up for vote again since the mandatory 6-month waiting period has passed since the last vote and this RFC targets a new major version of PHP.